Make index queue bigger. (#2322)
Make index queue bigger. (#2322)

When a large Prometheus starts up fresh it can take many minutes
to warmup and clear out the index queue. A larger queue means less
blocking, bigger batches and cuts down startup time by ~50%.
Stackdriver/stackdriver-prometheus,Colstuwjx/prometheus,yanghongkjxy/prometheus,amorken/prometheus,yanghongkjxy/prometheus,GoogleCloudPlatform/prometheus,kangwoo/prometheus,Colstuwjx/prometheus,GoogleCloudPlatform/prometheus,gottwald/prometheus,dsymonds/prometheus,prometheus/prometheus,agaoglu/prometheus,Gouthamve/prometheus,yanghongkjxy/prometheus,kzittritsch/prometheus,kangwoo/prometheus,gottwald/prometheus,kangwoo/prometheus,prometheus/prometheus,Colstuwjx/prometheus,agaoglu/prometheus,Gouthamve/prometheus,alileza/prometheus,Gouthamve/prometheus,tomwilkie/prometheus,alileza/prometheus,dsymonds/prometheus,brancz/prometheus,tomwilkie/prometheus,dsymonds/prometheus,Gouthamve/prometheus,Stackdriver/stackdriver-prometheus,gottwald/prometheus,JavierZunzunegui/prometheus,JavierZunzunegui/prometheus,amorken/prometheus,kangwoo/prometheus,amorken/prometheus,keegancsmith/prometheus,tomwilkie/prometheus,AlekSi/prometheus,brancz/prometheus,yanghongkjxy/prometheus,keegancsmith/prometheus,kzittritsch/prometheus,kzittritsch/prometheus,JavierZunzunegui/prometheus,agaoglu/prometheus,gottwald/prometheus,GoogleCloudPlatform/prometheus,SaltedMan/prometheus-annotated,Stackdriver/stackdriver-prometheus,Colstuwjx/prometheus,Conorbro/prometheus,prometheus/prometheus,keegancsmith/prometheus,amorken/prometheus,AlekSi/prometheus,alileza/prometheus,prometheus/prometheus,alileza/prometheus,SaltedMan/prometheus-annotated,GoogleCloudPlatform/prometheus,prometheus/prometheus,brancz/prometheus,keegancsmith/prometheus,alileza/prometheus,JavierZunzunegui/prometheus,agaoglu/prometheus,AlekSi/prometheus,kzittritsch/prometheus,Conorbro/prometheus,dsymonds/prometheus,Conorbro/prometheus,tomwilkie/prometheus,SaltedMan/prometheus-annotated,Conorbro/prometheus,SaltedMan/prometheus-annotated,GoogleCloudPlatform/prometheus,AlekSi/prometheus,keegancsmith/prometheus,Stackdriver/stackdriver-prometheus,brancz/prometheus